1. Field of the Invention
The present invention relates to etching techniques. More particularly, the present invention relates to a method of simultaneously controlling the ADI-AEI CD differences of openings having different sizes, as well as to an etching process utilizing the same method. The ADI-AEI CD difference of an opening is defined hereinafter as the difference of the after-development-inspection critical dimension (ADI CD) and the after-etching-inspection critical dimension (AEI-CD) of the opening, and is sometimes simply called a “size difference” in the following descriptions.
2. Description of the Related Art
As the integration degree of IC devices is always required higher, the dimensions of semiconductor devices have to be reduced unceasingly. The most intuitive method to reduce the pattern size is to utilize high-resolution lithography, but the high-resolution techniques are difficult and costly to use due to the limitations in optics. Particularly, the ADI CD of an opening pattern is much more difficult to reduce with lithographic techniques only as compared with a line pattern of the same width. Therefore, the etching recipe of the subsequent opening-etching step using the opening pattern as a mask is usually adjusted to make the AEI CD relatively smaller than the ADI CD.
However, in the cases where the etching recipe is adjusted to reduce the AEI CDs of openings having different sizes, the ADI-AEI CD differences of the openings are difficult to control as required. For example, when the AEI CD of a square contact opening is reduced in a process of simultaneously forming a square contact for a source/drain (S/D) region and a larger share contact for a gate and an S/D region beside the gate, the AEI CD of the share contact opening is reduced more. When the AEI CD of a share contact opening is overly reduced, the share contact formed therein has an overly high resistance lowering the operation speed, or even disconnects with the target gate or S/D region to form a broken circuit. On the contrary, when the sizes of the two types of openings both are reduced insufficiently, misconnections may occur. Hence, the size differences of the two types of contact openings both have to be controlled suitably.
Similarly, in other kinds of opening processes where the AEI CDs of openings with different sizes have to be reduced simultaneously, the ADI-AEI CD differences of the openings have to be controlled simultaneously to meet the requirements.